Produced by Susan Mallie, Dena Goldstein and Mead Stone
[This show was originally broadcast on April 21, 2012. It was updated on Dec. 22.]

(CBS News) Barb Thompson has lived on her farm in Spokane, Washington, breeding horses, for more than 30 years.

She was just 19 when Ronda was born. Barb's husband left three years later, leaving the newly-single mom with an energetic little girl to raise.

"We got her a pony. She was just hell on wheels. And then she went to the bigger horses and jumping," Thompson told "48 Hours Mystery" correspondent Peter Van Sant.

The farm is a place where Thompson draws strength, but a place she's had to leave over and over as she tries to unravel the mystery of her daughter's death.

It was on Dec, 16, 1998, in Toledo, Washington. Ronda Reynolds, then 33 years old, was discovered in her home on Twin Peaks Drive, dead of a gunshot wound to the head. Her death was ruled a suicide, but one person wasn't buying it.

"It was suicide from the beginning. They already had it labeled, but there is something inside of you that says something's wrong," Thompson cried. "I was going to find the truth, whatever that truth was."

On this particular day in October 2011, Thompson is stopping in Seattle to pick up an old friend: Best-selling true-crime writer Ann Rule.

They're an unlikely duo who never would have met had it not been for Ronda's troubling death.

"I remember hearing it on the radio that December in 1998. ...And it just hit me wrong then. I said, 'Uh-uh. This -- this isn't quite right,'" Rule told Van Sant. "Barb...called me in the first year."

"She just called you out of the blue?" Van Sant asked.

"Oh, yeah. Yeah."

Thompson convinced the world-famous author to join her in investigating Ronda's death.

It took 10 years of intense legal wrangling, but finally in 2011, a coroner's inquest was launched to decide once and for all if Ronda's death was a suicide or a homicide.

Thompson says the daughter she raised could never have taken her own life.

"I know my child. I know her zest for life," she said.

Ronda's zest for life would end up leading her down an unusual path.

"She must have been four or five years old when I realized her one dream in life was law enforcement," Thompson continued.

Ronda was 22 when she achieved her dream, becoming the youngest female state patrol trooper in Washington history. Just a year after joining, she a married ex-Marine and fellow trooper Mark Liburdi.

"Mark was a single parent with three children. And she fell in love with these three children," said Thompson.

But in 1994, Ronda Reynolds' life suddenly began to unravel. Injured on the job, she was accused of taking both disability and her regular pay. Ronda claimed it was all an innocent mistake.

"But sadly," Thompson explained, "it left a black mark on her name."

Ronda eventually resigned her dream job.

"During this time, her marriage was going downhill with Mark Liburdi," said Thompson.

Ronda and Liburdi sought counseling through their Jehovah's Witness church where the elder was none other than Ron Reynolds.

"And is it true you were a marriage counselor to them at one point?" Van Sant asked Ron Reynolds.

"I -- that's true," he replied.

Reynolds and his own wife, Catherine, were splitting up. And in the most unlikely of twists, counselor and counselee started their own romance.

"Ronda just called me up one day...telling me that she really liked me and she wanted to see me. And so from then on we started a relationship," he told Van Sant.

"You fell in love with her?"

"Uh huh, absolutely," Reynolds replied.

In January 1998, just five weeks after her divorce from Mark Liburdi was finalized, Ronda and Ron Reynolds were married. With her new husband came five stepsons.

Two of Reynolds' boys were full-blown teenagers, including 16-year-old Jonathan.

"It was a new mom, in our house and everything," he said. "There wasn't a lot of lovey-dovey stuff going on. But she was really friendly with us."

The family settled into a new home, with spectacular views of the twin peaks - Mount Rainier and Mount St. Helens. Reynolds was principal of the local elementary school. But just months after marrying, the relationship started to strain.